Method and apparatus for producing acoustic vibrations in fluids



E. c. COTTELL ETAL 3,176,954 ME D AND APPARATUS FOR PRODUCING USTIC VIBRATIONS IN FLUIDS Filed Jan. 5, 1961 April 6, 1965 ATTORNEY INVENTOR.

ERIC C. COTTE LL JOHN JACOBSJII United States Patent f METHUD AND APPARATUS FQR PERGDUQNG AQOUdTiC VEBRATEGNS EN FLEJEDS Eric E tlorttell, Rowayton, and Eohn dacohs HE, Darien, Conn, assignors to Sonic Engineering Corporation,

Stamford, @Conn, a corporation of Connecticut Filed .l'an. 5, 1961, Ser. No. 813,764 8 illaims. (Cl. 259-1) This invention relates to a method and apparatus for producing acoustic vibrations in a flowing liquid medium and, more particularly, an improved apparatus of the type described in the Cottell at al. patent US. 2,657,021, granted October 27, 1953. The Cottell et al. patent referred to above describes and claims a device which is often referred to as a liquid whistle. In the device, a liquid or mixture of liquids or liquids and suspended solids are pumped at high pressure and high speed through a nozzle forming a jet and strike the edge of a vibrating blade. Violent oscillation results and the device has been extremely useful in a number of industrial fields, such as emulsification and the like. The device of the Cottell patent is provided With a bell or other housing surrounding the vibrating blade and is described in connection with mixing tanks, discharging a material from the bell chamber either above or below the surface or" the liquid in the tank.

in spite of the wide commercial success of the Cottell device, certain problems have arisen. The device is not capable of adjustment during operation, although adjustment of jet-to-blade distance can be effected by disassembly of the device and changing the position of the blade. This, however, requires a shutdown of the apparatus, and, while this is no problem when the device is adjusted to operate with different materials as from one of low viscosity to high viscosity, it has proven difficult, in fact in some cases impossible, to maintain continuously peak acoustic efficiency. Thus, although the Cottell device is very useful, it still leaves room for improvement. The reason for the above problem is twofold. The first and most important reason is that contrary to prior thought the conditions downstream from the point of cavitation or development of acoustic energy markedly affect emciency. This effect was not realized at the time of the Cottell invention. The present invention provides an improved acoustic device which throughout the specification will be referred to by its more common term liquid whistle. Control of back pressure downstream from the point of cavitation makes possible a much more efiicient liquid whistle of the general type described in the Cottell patent, namely one where a jet of fluid strikes an obstruction, preferably blade-like, and capable of vibration.

The shape of the jet is not critical so long as it is unstable. Unstable jets are produced when one axis is substantially longer than the other. These jets will be referred to as relatively fiat jets although they are not necessarily in the form of ribbons of constant dimensions. Thus, for example it is possible to produce a substantially fiat jet by a series of small circular nozzles arranged in a line. While the individual small jets as they leave the nozzle are not flat, together they produce a jet which overall has the characteristic of flatness. It should also be realized that the fiat jet can be curved, the extreme resulting in an annular jet which is also unstable. All of these forms of unstable jets which have one axis or dimension that is larger than the other will be referred to as relatively fiat. The present invention is not useful if the jets have ares of the same length. Thus, for example, a perfectly round jet or a square or hexagonal jet are not sufficiently unstable to produce efiective liquid 3,.lib,%i atented Apr. 6, 1965 ice whistles, and such jets are not included in the present invention.

The liquid whistles of the present invention may have two adjustable quantities, namely jetto-blade distance and downstream back pressure. A third factor which is of importance but which normally is not continuously adjustable, is the dimensions of the chamber surrounding the jet and the blade. Different chamber dimensions will require different relative jet-to-blade distance and downstream pressure. It should be realized that it is the relative values of these two adjustable factors which produce maximum efficiency. However, there is a second reason why the original Cottell whistle, although constituting a great advance, still left room for improvement. For any particular type of nozzle and blade configuration there is an optimum jet-to-blade distance. This, however, holds only when the Other characteristics of the liquid remain constant, such as its velocity, viscosity, etc. Therefore, even if the whistle were built with an optimum jet-to-blade distance, if liquid velocity or What is more likely its other rheological characteristics change during operation the whistle efficiency will fall off. Therefore, for some operations, and especially in a whistle which is to be used for a number of diiferent fluids, it is desirable to be able to adjust the jet-to-blade distance during op eration. In a more specific form of the present invention this is provided and presents an advantage, although it is far less important than control of backstream pressure. It is, of course, possible to change the relation of jet-to-blade distance and downstream back pressure by varying only the former. However, if there is to be only one variable control it is far preferable to control the downstream pressure. After all, when changing from a fluid of one characteristic to a fluid of different characteristic operations have to be interrupted and it is perfectly possible to unscrew portions of the whistle and adjust the jet-to-blade distance for a new operation. However, the possibility of adjusting both jet-to-blade distance and downstream pressure during operation is prefered as this results in an instrument which is capable of the finest control for maximum efliciency under all operating conditions.

It has been stated that downstream back pressure and jet-to-blade distance must be adjusted for a particular fluid medium. This can be brought out by a typical example. Taking a liquid whistle with 300 psi. upstream from the jet and a downstream back pressure of 30 p.s.i. it is possible to locate areas with a fine probe near the blade where a vacuum of as high as 16" of mercury exists. It the upstream pressure is reduced the maximum cavitation efiiciency is no longer obtained and the device must again be tuned by reducing the downstream back pressure.

Reference has been made to the device of the present invention as a liquid whistle but the materials handled need not be, and more often than not are not a pure liquid. 0n the contrary one of the most important fields of utility of the invention is in emulsification where a plurality of liquids are present and homogenization where there are suspensions of solids in liquids. Mixtures of liquids and gases are also sometimes encountered. However, the invention does require that "there be at least sufficient liquids present so that the material as a whole has flow characteristics resembling a liquid. Thus the device will not operate with pure gases and no liquids. In such a case it will produce a sound but will not produce the high acoustic energy and cavitation for which it is of primary importance.

It is possible to use liquid whistles of the present invention to perform an entirely different function. The energies obtained by proper adjustment of downstream 3 back pressure are so great that the whistle may be used to test materials for fatigue and other properties.

In general, the present invention is not'concerned with exact design of throttling or .jet-to blade distance varying means. However, in the case of the latter, the setting should be quite precise and so" micrometric adjusting mechanisms Which are substantially free from backlash are desirable. A practically very effective device will be described below in conjunctionwith a specific descripf tion of the invention. It is also desirable-that the subs'tantially flat jets of the present invention have their long axis at least roughly parallel with the long dimensions of the blade. This is not to say that liquid whistles where there is not exact parallelism or where a diiie'rent shape of blade or obstruction is used, are not effective. However, to obtain the maximum energy with minimum power input it is advantageous to have the long dimensions of the jet and obstruction or blade substantially in the same direction.

. junction with the drawings in which:

FIG. 1 is an isometric view, partially broken away, of a liquid whistle of the present invention, and

FIG. 2 is a detailed plan view of the jet nozzle.

The liquid Whistle has a mainbody 1 in the form of a cylindrical forging of high tensile, noncorrosive materials, such as, for example, stainless steel. :Oneend is threaded and connects to the liquid line from a high pressure pump (not shown). The other end of the casting is enlarged, threaded and provided with a sealing shoulder 3. Centrally located is a flange 4 atone point of which there is provided a hole through which a screw 7 passes. This screw bears against the enlarged threaded end 3 and carries a movable nut 5. This screw is locked in adjustment by a knurled locking nut 8'.

Within the cylinder 1 is a tightly sealed piston 2 with a smaller central bore which at the upstream end is flared out. The other end carries a jet nozzle 9. A projection 6 of the nut extends into a shallow hole in the wall of the piston. with it the piston 2 and serves as the adjustment locating the position of the jet. V

A cylinder 10 is carried'by the end of the housingl. It carries a threaded cap 11 and blade clamping wedges I 21 which clamp the blade 12 when the cap is screwed tight. Additionally, the blade is kept from moving by pins which extend through the blade. Actuation of the screw 7 moves the piston 2 backward and forward to vary the distance from the jet nozzle 9 to the blade 25.2. At the same time, the projection 6 of the nut 5 prevents the piston 2 from turning, an important consideration be cause it is desirable as pointed out in the Cottell patent to keep the long dimension of the ribbon jet parallel to the blade.

On the downstream side, there is provided a pipe or housing 13 which, because it does not have to withstand as high pressure, may be made of plastic. This is connected to the housing 1 by means of the sealing ring 17 and clamping nut 18 which engages the threads of the enlarged end 3. Downstream from the blade, there is a throttling valve 22 which varies the back pressure of the downstream flow from the blade mounting.

The elements described above, are all that are required for manual operation of the invention.

independently adjustable, if desired, during operation of Rotation of the screw 7 moves the nut 5 and The relative p0 sition of jet and blade and downstream back pressure are the liquid whistle. Because of the greater precision possible by controlling downstream pressure as set out above, it is often desirable to adjust the blade to jet' distance manually, lock it withthe locking nut 8, and from then Thisoutput actuates a meter 16 which permits a measurement of the acoustic energy when the instrument is operating. In accordance with the meter reading, downstream throttling can be adjusted-until the desired maximum reading is obtained. This may also be coupled with some adjustment of the nozzle to blade distance as described above. An ordinary meter is shown, but any other indicating device may be used, for example, a standard-oscilloscope with a horizontal sweep set to a multiple or sub-multiple of the principal component of the principal acoustic vibration frequency of the liquid. For' production control purposes, the meter is entirely ade-' quate, but for research purposes, an oscilloscope also gives some further information as to the wave shape. In general, when the oscilloscope is used, it will be seen that as the adjustments of the instruments are operated, a sine wave is produced and at the point, or near the point or zone of highest eiiiciency, it will be seen that there are breakups in the smooth sine wave shape which indicate the violent cavitation which occurs 'at maximum acoustic efliciency. v a

The electrical signal obtained from the amplifier 15 may also be used for other purposes and a desirable automatic control" is efiected by using this signal to actuate the throttling valve 22 through conventional servo mechanisms indicated diagrammatically at 19. This permits an automatic maintenance of the instrument at maximum elficiency regardless of changes in characteristics of the material being treated, for example, viscosity changes due to temperature and the like, or to changes in velocity of flow or other factors which can aifect the efficiency of the instrument. It is an advantage of the present invention, that it is very flexible and can be used as a simple instrument with one or more manual controls, or as a more sophisticated instrument with acoustic energy indicators, and/or automatic control of' downstream pressure to maintain constant peak efficiency. The particular modification to be chosen is dictated by the requirements of the operation to be performed by the instrument and makes the present invention applicable in a wide range of operations.

The automatic control modification has been shown as automatically controlling downstream back pressure. Normally, this will give the best control, however, it is equally possible to use the signal with'suitable servo mechanisms to actuate the adjustment of jet-to-blade distance and, of course, the signal may be used to adjust both.

While the design of the servo mechanism to be used is not a part of the present invention, it should be noted that the result of adjustment normally is to increase acoustic energy to a high point or plateau and further adjustment in the same direction will then result in a decrease. Simple servo mechanisms, therefore, are usable ifthey operate on or near one or the other of the edges of the acoustic energy graph. It is possible with more sophisticated servo controls'to have the control reverse itself if it is past the plateau. Ordinarily, the maximum plateau, however, is sufliciently broad so that servo mechanisms of a simple type may be used. Alternatively, and for practical purposes this will often be the most economical choice, an indicator may be used for initially setting the adjustment near the proper point and automatic adjustments are relied on only to take care of the normally much smaller variations from maximum efiiciency during operation. The question of the degree of elaborateness of automatic control is almost entirely one of economics and, often, the most expensive and complicated control mechanisms will not be warranted as some degree of human supervision is almost always necessary in any installation.

It has been pointed out above that the substantially fiat jets are preferably aligned so that their long dimensions correspond to those of the blade they strike. While relatively flat jets need not have parallel surfaces, that is to say they need not be perfect ribbons, the etficiency of the liquid whistle is greater the more closely the jet is in the form of a really flat ribbon. Prior to the Cottell patent it had been though that the way to produce a ribbon jet would be to employ a flat orifice. This has been proven to be a completely false assumption. If an elongated rectangular orifice is used the jet instead of being in the form of a ribbon looks like a dumbbell having greater thicknesses at the corners and a narrower width between. To produce more nearly fiat ribbon jets the nozzle orifice should be properly shaped. In general this is curved as shown in FIG. 2, the curvature being adjusted so that it compensates as nearly as possible for the dumbbell eliect of a rectangular nozzle. The exact shape of the nozzle is not sharply critical as the efliciency of the device does not fall off immediately if the jet departs somewhat from the form of a perfect ribbon. This is an advantage as it is not necessary constantly to change nozzles. However, if there are going to be very wide ditierences in the flow characteristics of the medium it is advantageous to provide a nozzle which will produce as nearly a flat jet as is convenient. During operation small changes in flow characteristics will not affect the efiiciency sufficiently to require substitution of a diiferent nozzle.

We claim:

1. Apparatus for producing acoustic vibrations in a flowing liquid which comprises a nozzle to produce a jet of liquid, a blade-like w'bratory element positioned to encounter said jet so that said vibratory element is caused to vibrate upon impingement by said jet, a chamber surrounding said nozzle and said vibratory element and means positioned downstream of said nozzle for adjusting the liquid pressure in said chamber surrounding said vibratory element.

2. Apparatus in accordance with claim 1 wherein means are provided for adjusting nozzle-to-vibratory element distance.

3. Apparatus in accordance with claim 1 wherein said means for adjusting the pressure in said chamber is a flow-control means positioned in fluid communication with said chamber downstream of said nozzle.

4. Apparatus in accordance with claim 1 wherein means actuatable from outside of said chamber are provided for adjusting the nozzle-to-vibratory element distance.

5. Apparatus in accordance with claim 1 wherein said nozzle is provided by a piston with a liquid inlet at one end, said piston having a central hollow conduit between said inlet at said one end and said nozzle at the other end, an outer housing surrounding said piston and provided with an opening, an adjustable, movable element in said opening and guided thereby and means for fixedly attaching said adjustable, movable element to said piston whereby movement of said adjustable, movable element causes movement of said piston.

6. Apparatus in accordance with claim 1 wherein a piezoelectric transducer is associated with said chamber and adapted to produce an electric signal responsive to pressure changes Within said chamber, electronic amplifying means, connecting means from said transducer to said amplifying means to transmit electric signals from said transducer to said amplifying means, servo-actuated driving means for said means for adjusting the liquid pressure within said chamber and means for connecting the output of said amplifying means to said driving means to actuate said means to adjust the liquid pressure within said chamber.

7. In an operation wherein acoustic vibrations are generated in a flowing liquid by forming a jet of liquid, causing said jet of liquid to impinge upon the edge of a bladelike vibratory element provided in a chamber to cause said vibratory element to vibrate and to create acoustic vibrations in the surrounding liquid within said chamber, the improvement which comprises controlling the generation of acoustic vibrations within the liquid within said chamber surrounding said vibratory element by adjusting the pressure of the liquid surrounding said vibratory element by restricting the flow of liquid from said chamber downstream of said jet.

8. In an operation wherein acoustic vibrations are generated in a flowing liquid by forming a ribbon-like jet of liquid, causing said jet of liquid to impinge upon the edge of a blade like vibratory element provided in a chamber to cause said vibratory element to vibrate and to create acoustic vibrations in the surrounding liquid within said chamber, the improvement which comprises controlling the generation of acoustic vibrations within the liquid within said chamber surrounding said vibratory element by adjusting the pressure of the liquid within said chamber surrounding said vibratory element by restricting the flow of liquid from said chamber downstream of said jet and by adjusting the length of said ribbon-like jet of liquid before said jet impinges upon said vibratory element.

References Cited in the file of this patent UNITED STATES PATENTS 1,236,002 Nivling Aug. 7, 1917 2,657,021 .Cottelt' et a1 Oct. 27, 1953 2,713,998 Eicken July 26, 1955 2,832,018 Laub Apr. 22, 1958 

1. APPARATUS FOR PRODUCING ACOUSTIC VIBRATIONS IN A FLOWING LIQUID WHICH COMPRISES A NOZZLE TO PRODUCE A JET OF LIQUID, A BLADE-LIKE VIBRATORY ELEMENT POSITIONED TO ENCOUNTER SAID JET SO THAT SAID VIBRATORY ELEMENT IS CAUSED TO VIBRATE UPON IMPINGEMENT BY SAID JET, A CHAMBER SURROUNDING SAID NOZZLE AND SAID VIBRATORY ELEMENT AND MEANS POSITIONED DOWNSTREAM OF SAID NOZZLE FOR ADJUSTING THE LIQUID PRESSURE IN SAID CHAMBER SURROUNDING SAID VIBRATORY ELEMENT. 